Hello,
the GCC construct __attribute__((aligned)) is defined to set alignment to "the default alignment for the target architecture" according to the GCC documentation: The default alignment is sufficient for all scalar types, but may not be enough for all vector types on a target that supports vector operations. The default alignment is fixed for a particular target ABI. clang currently hard-codes an alignment of 16 bytes for that construct, which is correct on some platforms (including X86), but wrong on others (including SystemZ). Since this value is ABI-relevant, it is important to get correct for compatibility purposes. The following patch adds a new TargetInfo member "DefaultAlign" that targets can set to the appropriate default __attribute__((aligned)) value. Note that I'm deliberately *not* using the existing "SuitableAlign" value, which is used to set the pre-defined macro __BIGGEST_ALIGNMENT__, since those two values may not be the same on all platforms. In fact, on X86, __attribute__((aligned)) always uses 16-byte alignment, while __BIGGEST_ALIGNMENT__ may be larger if AVX-2 or AVX-512 are supported. (This is actually not yet correctly implemented in clang either.) The patch provides a value for DefaultAlign only for SystemZ, and leaves the default for all other targets at 16, which means no visible change in behavior on all other targets. (The value is still wrong for some other targets, but I'd prefer to leave it to the target maintainers for those platforms to fix and test.) (See attached file: clang-align-attribute) Mit freundlichen Gruessen / Best Regards Ulrich Weigand -- Dr. Ulrich Weigand | Phone: +49-7031/16-3727 STSM, GNU/Linux compilers and toolchain IBM Deutschland Research & Development GmbH Vorsitzende des Aufsichtsrats: Martina Koederitz | Geschäftsführung: Dirk Wittkopp Sitz der Gesellschaft: Böblingen | Registergericht: Amtsgericht Stuttgart, HRB 243294
clang-align-attribute
Description: Binary data
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